Double-configuration basket structure for improving obdurability of titanium alloy friction welding joint and preparation method of double-configuration basket structure

Abstract

The invention discloses a double-configuration basket structure for improving the obdurability of a titanium alloy friction welding joint, the grain boundary in the structure is a lamellar primary alpha phase, the intracrystalline is a needle-shaped secondary alpha 'phase, and the primary alpha phase and the secondary alpha' phase are uniformly distributed on a beta-phase matrix in a staggered manner. The invention further discloses a preparation method of the double-configuration basket structure for improving the obdurability of the titanium alloy friction welding joint. According to the method, by constructing a double-configuration basket structure of a grain boundary flaky primary alpha phase and an intragranular needle-shaped secondary alpha 'phase, the strength and toughness of the joint are synchronously and remarkably improved, and a new thought is provided for solving the problem of low-toughness fracture of an original welding joint.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy welded joint structure, and in particular relates to a dual-configuration basket structure for improving the toughness of titanium alloy friction welded joints, and also relates to a preparation method of the structure. Background Art

[0002] Titanium alloy materials have become an ideal choice in the aviation field due to their excellent specific strength, high-temperature mechanical properties, creep resistance, and corrosion resistance. High-toughness titanium alloys are mainly used in the preparation of integral blades and fuselage structural parts of aircraft engines due to their excellent toughness and good comprehensive mechanical properties. Linear friction welding (LFW) is a high-quality solid-phase welding technology that can effectively avoid solidification defects such as pores and inclusions in fusion welding, and is not constrained by the welding section. Preformed semi-finished parts can be directly welded into integral joints. However, the equiaxed crystals in the weld zone of the joint promote crack initiation and the spherical dispersed particles in the crystals accelerate crack propagation, resulting in low-toughness cleavage fracture at the joint, which restricts the widespread application of linear friction welding technology. The conventional basketweave structure configuration has excellent strength and toughness, but it is difficult to meet the requirements of higher strength and toughness mechanical properties. Summary of the invention

[0003] The purpose of the present invention is to provide a dual-configuration basket structure for improving the toughness of a titanium alloy friction welding joint, thereby solving the problem of low-toughness fracture of the joint in the prior art.

[0004] Another object of the present invention is to provide a method for preparing a dual-configuration basket structure for improving the toughness of a titanium alloy friction welded joint.

[0005] The technical solution adopted by the present invention is to improve the strength and toughness of the titanium alloy friction welding joint with a dual-configuration basket structure, in which the grain boundaries are lamellar primary α phase and the crystals are needle-shaped secondary α′ phase, and the primary α phase and the secondary α′ phase are evenly staggered on the β phase matrix.

[0006] The present invention is characterized in that: The volume fraction of the lamellar primary α phase is 10% to 25%, the volume fraction of the needle-shaped secondary α′ phase is 40% to 60%, and the volume fraction of the β phase matrix is ​​25% to 35%. The total volume fraction is 100%.

[0007] The length of the lamellar primary α phase is 6μm~18μm, and the aspect ratio is 5:1~15:1.

[0008] The length of the needle-shaped secondary α′ phase is 3μm~10μm, and the aspect ratio is 10:1~20:1.

[0009] The phase difference between adjacent grains in the basketweave structure is less than 10°, accounting for 20% to 30%, and greater than 10°, accounting for 70% to 80%. Among them, the orientation difference in the large-angle grain boundaries of the α phase is 30°, accounting for 5% to 15%, 60° accounting for 45% to 55%, and 90° accounting for 35% to 45%.

[0010] Another technical solution adopted by the present invention is a method for preparing a dual-configuration basket structure for improving the toughness of a titanium alloy friction welded joint, which is specifically implemented according to the following steps: Step 1, linear friction welding is performed on TC21 titanium alloy to obtain a TC21 titanium alloy sample with an original welded joint; Step 2: After pre-treating the titanium alloy sample in step 1, the sample is subjected to electric pulse treatment using preset processing parameters to form a dual-configuration basketweave structure in the joint weld area.

[0011] Another technical solution of the present invention is also characterized in that: The pretreatment in step 2 is as follows: the titanium alloy linear friction welding sample is cut into pieces with a size of 70×12×3 mm by wire cutting technology. 3 The sample is ground on the surface by a grinder to control the surface processing accuracy within 0.01mm.

[0012] The specific electric pulse treatment in step 2 is as follows: the pretreated sample is fixed between two copper electrodes of the electric pulse device, and the electric pulse treatment parameter range is: pulse voltage 50V~100V, pulse frequency 200Hz~350Hz, pulse time 60s~130s, root mean square current density 6×10 6 A / m 2 ~12×10 6 A / m 2 .

[0013] The beneficial effect of the present invention is that the present invention constructs a dual-configuration basket structure of lamellar primary α phase at the grain boundary and needle-shaped secondary α′ phase in the crystal, thereby significantly improving the strength and toughness of the joint and providing a new idea for solving the problem of low-toughness fracture of the original welded joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a principle diagram of the relationship between organization and toughness in the present invention; Figure 2 is a microstructure diagram of the weld area before and after the joint electric pulse treatment in Example 4 of the present invention; Figure 3 is a distribution diagram of orientation differences after the joint is treated with electric pulses in Example 4 of the present invention; Figure 4 is a graph of impact toughness values ​​of the joint under different treatment methods in the present invention; Figure 5 is an impact fracture morphology diagram of a welded joint in Example 4 of the present invention; Figure 6 This is the impact fracture morphology of the joint treated with electric pulse in Example 4 of the present invention. DETAILED DESCRIPTION

[0015] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] The preparation method of the dual-configuration basket structure for improving the toughness of titanium alloy friction welding joints of the present invention is specifically implemented according to the following steps: Step 1, linear friction welding is performed on TC21 titanium alloy to obtain a TC21 titanium alloy sample with an original welded joint; Step 2, after pre-treating the titanium alloy sample in step 1, the sample is subjected to electric pulse treatment using preset processing parameters to form a dual-configuration basketweave structure in the joint weld area; The pretreatment in step 2 is as follows: the titanium alloy linear friction welding sample is cut into pieces with a size of 70×12×3 mm by wire cutting technology. 3 The sample is ground on the surface by a grinder to control the surface processing accuracy within 0.01mm.

[0017] The specific electric pulse treatment in step 2 is as follows: the pretreated sample is fixed between two copper electrodes of the electric pulse device, and the electric pulse treatment parameter range is: pulse voltage 50V~100V, pulse frequency 200Hz~350Hz, pulse time 60s~130s, root mean square current density 6×10 6 A / m 2 ~12×10 6 A / m 2 ; The dual-configuration basket weft structure of the weld zone of the joint obtained in step 2 has a grain boundary of lamellar primary α phase and a needle-shaped secondary α′ phase in the grain, both of which are evenly staggered on the β phase matrix. The volume fraction of the lamellar primary α phase is 10%~25%, the length is 6μm~18μm, and the aspect ratio is 5:1~15:1; the volume fraction of the needle-shaped secondary α′ phase is 40%~60%, the length is 3μm~10μm, and the aspect ratio is 10:1~20:1; the volume fraction of the β phase matrix is ​​25%~35%; the phase difference of adjacent grains in the basket weft structure configuration is less than 10° (small angle grain boundary), accounting for 20%~30%, and greater than 10° (large angle grain boundary) accounting for 70%~80%; among them, the orientation difference in the large angle grain boundary of the α phase is 30°, accounting for 5%~15%, and 60° accounting for 45%~60%. 55%, and 35% to 45% at 90°.

[0018] After electric pulse treatment, the mechanical properties of the joint were tested and the microstructure of the weld area was characterized, which confirmed that a dual-configuration basketweave structure was formed in the weld area of ​​the joint. The experimental data obtained were integrated and analyzed, confirming the feasibility of this microstructure configuration in regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0019] Example 1 The preparation method of the dual-configuration basket structure for improving the toughness of the titanium alloy friction welded joint is specifically implemented according to the following steps: Step 1, linear friction welding is performed on TC21 titanium alloy to obtain a TC21 titanium alloy sample with an original welded joint; Step 2: Pre-treat the titanium alloy sample in step 1 (cut the titanium alloy linear friction welding sample into pieces with a size of 70×12×3 mm by wire cutting technology). 3 The sample was ground by a grinder to control the surface processing accuracy within 0.01 mm. Then, the sample was subjected to electric pulse treatment according to the preset processing parameters (the pre-treated strip sample was fixed between two copper electrodes of the electric pulse device. The electric pulse treatment parameter range was: pulse voltage 60 V, pulse frequency 190 Hz, pulse time 75 s, root mean square current density 6.88 × 10 6 A / m 2 ), so that the joint weld area forms a dual-configuration basket structure; Step 3, the joint obtained in step 2 after the electric pulse treatment is subjected to mechanical property testing and weld zone microstructure characterization, confirming that a dual-configuration basketweave microstructure is formed in the weld zone of the joint; The characterization results of the microstructure of the weld zone in step 3 are as follows: the grain boundaries in the weld zone are lamellar primary α phase, and the intragranular is needle-shaped secondary α′ phase, both of which are evenly staggered on the β phase matrix. The volume fraction of the lamellar primary α phase is 17%, the length is 6μm, and the aspect ratio is 5:1; the volume fraction of the needle-shaped secondary α′ phase is 51%, the length is 3μm, and the aspect ratio is 10:1; the volume fraction of the β phase matrix is ​​32%. The phase difference of adjacent grains in the basketweave structure configuration is less than 10° (small angle grain boundary) accounting for 25.4%, and greater than 10° (large angle grain boundary) accounting for 74.6%; among them, the orientation difference of the large angle grain boundary of the α phase is 30° accounting for 10.5%, 60° accounting for 50.2%, and 90° accounting for 39.3%. In summary, the weld zone of the TC21 titanium alloy linear friction welding joint after electric pulse treatment forms a dual-configuration basketweave structure.

[0020] Step 4: Integrate and analyze the experimental data obtained in step 3 to confirm the feasibility of this configuration in regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0021] In step 4, it was analyzed that after the electric pulse treatment, the impact toughness of the joint with the dual-configuration basket structure was greatly improved compared with the welded joint, from 16.7 J / cm 2 to 54.7 J / cm 2 , reaching 89.5% of the TC21 titanium alloy joint parent material. This configuration has an obvious effect on regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0022] Example 2 The preparation method of the dual-configuration basket structure for improving the toughness of the titanium alloy friction welded joint is specifically implemented according to the following steps: Step 1, linear friction welding is performed on TC21 titanium alloy to obtain a TC21 titanium alloy sample with an original welded joint; Step 2: Pre-treat the titanium alloy sample in step 1 (cut the titanium alloy linear friction welding sample into pieces with a size of 70×12×3 mm by wire cutting technology). 3 The sample was ground by a grinder to control the surface processing accuracy within 0.01 mm. Then, the sample was subjected to electric pulse treatment according to the preset processing parameters (the pre-treated strip sample was fixed between the two copper electrodes of the electric pulse device. The electric pulse treatment parameter range was: pulse voltage 60 V, pulse frequency 220 Hz, pulse time 75 s, root mean square current density 7.31 × 10 6 A / m 2 ), so that the joint weld area forms a dual-configuration basket structure; Step 3, the joint obtained in step 2 after the electric pulse treatment is subjected to mechanical property testing and weld zone microstructure characterization, confirming that a dual-configuration basketweave microstructure is formed in the weld zone of the joint; The characterization results of the microstructure of the weld zone in step 3 are as follows: the grain boundary in the weld zone is a lamellar primary α phase, and the intragranular is a needle-shaped secondary α′ phase, both of which are evenly staggered on the β phase matrix. The volume fraction of the lamellar primary α phase is 14%, the length is 8μm, and the aspect ratio is 8:1; the volume fraction of the needle-shaped secondary α′ phase is 55%, the length is 5μm, and the aspect ratio is 12:1; the volume fraction of the β phase matrix is ​​31%. The phase difference of adjacent grains in the basketweave structure configuration is less than 10° (small-angle grain boundary) accounting for 24.7%, and greater than 10° (large-angle grain boundary) accounting for 75.3%; among them, the orientation difference in the large-angle grain boundary of the α phase is 30° accounting for 11.3%, 60° accounting for 50.6%, and 90° accounting for 38.1%. In summary, the weld zone of the TC21 titanium alloy linear friction welding joint after electric pulse treatment forms a dual-configuration basketweave structure.

[0023] Step 4: Integrate and analyze the experimental data obtained in step 3 to confirm the feasibility of this configuration in regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0024] In step 4, it was analyzed that after the electric pulse treatment, the impact toughness of the joint with the dual-configuration basket structure was greatly improved compared with the welded joint, from 16.7 J / cm 2 to 55.1 J / cm 2 , reaching 90.2% of the TC21 titanium alloy joint parent material. This configuration has an obvious effect on regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0025] Example 3 The preparation method of the dual-configuration basket structure for improving the toughness of the titanium alloy friction welded joint is specifically implemented according to the following steps: Step 1, linear friction welding is performed on TC21 titanium alloy to obtain a TC21 titanium alloy sample with an original welded joint; Step 2: Pre-treat the titanium alloy sample in step 1 (cut the titanium alloy linear friction welding sample into pieces with a size of 70×12×3 mm by wire cutting technology). 3 The sample was ground by a grinder to control the surface processing accuracy within 0.01 mm. Then, the sample was subjected to electric pulse treatment according to the preset processing parameters (the pre-treated strip sample was fixed between two copper electrodes of the electric pulse device. The electric pulse treatment parameter range was: pulse voltage 60 V, pulse frequency 250 Hz, pulse time 65 s, root mean square current density 7.81 × 10 6 A / m 2 ), so that the joint weld area forms a dual-configuration basket structure; Step 3, the joint obtained in step 2 after the electric pulse treatment is subjected to mechanical property testing and weld zone microstructure characterization, confirming that a dual-configuration basketweave microstructure is formed in the weld zone of the joint; The characterization results of the microstructure of the weld zone in step 3 are as follows: the grain boundary in the weld zone is a lamellar primary α phase, and the intragranular is a needle-shaped secondary α′ phase, both of which are evenly staggered on the β phase matrix. The volume fraction of the lamellar primary α phase is 19%, the length is 10μm, and the aspect ratio is 10:1; the volume fraction of the needle-shaped secondary α′ phase is 56%, the length is 6μm, and the aspect ratio is 15:1; the volume fraction of the β phase matrix is ​​25%. The phase difference of adjacent grains in the basketweave structure configuration is less than 10° (small-angle grain boundary) accounting for 27.9%, and greater than 10° (large-angle grain boundary) accounting for 72.1%; among them, the orientation difference of the large-angle grain boundary of the α phase is 30° accounting for 12.6%, 60° accounting for 51.3%, and 90° accounting for 36.1%. In summary, the weld zone of the TC21 titanium alloy linear friction welding joint after electric pulse treatment forms a dual-configuration basketweave structure.

[0026] Step 4: Integrate and analyze the experimental data obtained in step 3 to confirm the feasibility of this configuration in regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0027] In step 4, it was analyzed that after the electric pulse treatment, the impact toughness of the joint with the dual-configuration basket structure was greatly improved compared with the welded joint, from 16.7 J / cm 2 to 54.1 J / cm 2 , reaching 88.5% of the TC21 titanium alloy joint parent material. This configuration has an obvious effect on regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0028] Example 4 The preparation method of the dual-configuration basket structure for improving the toughness of the titanium alloy friction welded joint is specifically implemented according to the following steps: Step 1, linear friction welding is performed on TC21 titanium alloy to obtain a TC21 titanium alloy sample with an original welded joint; Step 2: Pre-treat the titanium alloy sample in step 1 (cut the titanium alloy linear friction welding sample into pieces with a size of 70×12×3 mm by wire cutting technology). 3 The sample was ground by a grinder to control the surface processing accuracy within 0.01 mm. Then, the sample was subjected to electric pulse treatment according to the preset processing parameters (the pre-treated strip sample was fixed between two copper electrodes of the electric pulse device. The electric pulse treatment parameter range was: pulse voltage 60 V, pulse frequency 250 Hz, pulse time 75 s, root mean square current density 7.19 × 10 6 A / m 2 ), so that the joint weld area forms a dual-configuration basket structure; Step 3, the joint obtained in step 2 after the electric pulse treatment is subjected to mechanical property testing and weld zone microstructure characterization, confirming that a dual-configuration basketweave microstructure is formed in the weld zone of the joint; The characterization results of the microstructure of the weld zone in step 3 are as follows: the grain boundaries in the weld zone are lamellar primary α phase, and the crystals are needle-shaped secondary α′ phase, which are evenly distributed on the β phase matrix. Figure 2 As shown in the figure, the volume fraction of the lamellar primary α phase is 12%, the length is 18μm, and the aspect ratio is 15:1; the volume fraction of the needle-shaped secondary α′ phase is 59%, the length is 10μm, and the aspect ratio is 20:1; the volume fraction of the β phase matrix is ​​29%. The phase difference of adjacent grains in the basketweave structure configuration is less than 10° (small-angle grain boundary) accounting for 24.2%, and greater than 10° (large-angle grain boundary) accounting for 75.8%; among them, the orientation difference of the large-angle grain boundary of the α phase is 30° accounting for 11%, 60° accounting for 49.3%, and 90° accounting for 39.7%. In summary, the dual-configuration basketweave structure is formed in the weld zone of the TC21 titanium alloy linear friction welding joint after electric pulse treatment.

[0029] Step 4: Integrate and analyze the experimental data obtained in step 3 to confirm the feasibility of this configuration in regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0030] In step 4, it was analyzed that after the electric pulse treatment, the impact toughness of the joint with the dual-configuration basket structure was greatly improved compared with the welded joint, from 16.7 J / cm 2 to 55.3 J / cm 2 , reaching 90.5% of TC21 titanium alloy joint parent material, such as Figure 4 The impact fracture morphology of the TC21 linear friction welding joint before and after heat treatment is shown in Figure 5 , Figure 6 As shown in the figure, the joint changes from cleavage fracture mode to ductile fracture mode, and the toughness is greatly improved. Figure 1 The principle of the strength and toughness mechanism of the dual-configuration basketweave structure is demonstrated. It can be seen that the interlaced lamellar structure of the basketweave structure in this configuration increases the crack propagation path, and the fine needle-like structure in the crystal disperses the stress field at the crack tip, absorbs more energy, and achieves joint strength and toughness, further confirming the feasibility of this configuration in regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0031] Example 5 The preparation method of the dual-configuration basket structure for improving the toughness of the titanium alloy friction welded joint is specifically implemented according to the following steps: Step 1, linear friction welding is performed on TC21 titanium alloy to obtain a TC21 titanium alloy sample with an original welded joint; Step 2: Pre-treat the titanium alloy sample in step 1 (cut the titanium alloy linear friction welding sample into pieces with a size of 70×12×3 mm by wire cutting technology). 3 The sample was ground by a grinder to control the surface processing accuracy within 0.01 mm. Then, the sample was subjected to electric pulse treatment according to the preset processing parameters (the pre-treated strip sample was fixed between two copper electrodes of the electric pulse device. The electric pulse treatment parameter range was: pulse voltage 60 V, pulse frequency 270 Hz, pulse time 80 s, root mean square current density 7.97 × 10 6 A / m 2 ), so that the joint weld area forms a dual-configuration basket structure; Step 3, the joint obtained in step 2 after the electric pulse treatment is subjected to mechanical property testing and weld zone microstructure characterization, confirming that a dual-configuration basketweave microstructure is formed in the weld zone of the joint; The characterization results of the microstructure of the weld zone in step 3 are as follows: the grain boundary in the weld zone is a lamellar primary α phase, and the intragranular is a needle-shaped secondary α′ phase, both of which are evenly staggered on the β phase matrix. The volume fraction of the lamellar primary α phase is 17%, the length is 14μm, and the aspect ratio is 12:1; the volume fraction of the needle-shaped secondary α′ phase is 56%, the length is 7μm, and the aspect ratio is 16:1; the volume fraction of the β phase matrix is ​​27%. The phase difference of adjacent grains in the basket structure configuration is less than 10° (small angle grain boundary) accounting for 27.3%, and greater than 10° (large angle grain boundary) accounting for 72.7%; among them, the orientation difference in the large angle grain boundary of the α phase is 30° accounting for 10.1%, 60° accounting for 49.6%, and 90° accounting for 40.3%. In summary, the weld zone of the TC21 titanium alloy linear friction welding joint after electric pulse treatment forms a dual-configuration basket structure.

[0032] Step 4: Integrate and analyze the experimental data obtained in step 3 to confirm the feasibility of this configuration in regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0033] In step 4, it was analyzed that after the electric pulse treatment, the impact toughness of the joint with the dual-configuration basket structure was greatly improved compared with the welded joint, from 16.7 J / cm 2 to 54.9 J / cm 2 , reaching 89.8% of the TC21 titanium alloy joint parent material. This configuration has a significant effect on regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0034] Example 6 The preparation method of the dual-configuration basket structure for improving the toughness of the titanium alloy friction welded joint is specifically implemented according to the following steps: Step 1, linear friction welding is performed on TC21 titanium alloy to obtain a TC21 titanium alloy sample with an original welded joint; Step 2: Pre-treat the titanium alloy sample in step 1 (cut the titanium alloy linear friction welding sample into pieces with a size of 70×12×3 mm by wire cutting technology). 3 The sample was ground by a grinder to control the surface processing accuracy within 0.01 mm. Then, the sample was subjected to electric pulse treatment according to the preset processing parameters (the pre-treated strip sample was fixed between two copper electrodes of the electric pulse device. The electric pulse treatment parameter range was: pulse voltage 60 V, pulse frequency 300 Hz, pulse time 80 s, root mean square current density 8.27 × 10 6 A / m 2 ), so that the joint weld area forms a dual-configuration basket structure; Step 3, the joint obtained in step 2 after the electric pulse treatment is subjected to mechanical property testing and weld zone microstructure characterization, confirming that a dual-configuration basketweave microstructure is formed in the weld zone of the joint; The characterization results of the microstructure of the weld zone in step 3 are as follows: the grain boundary in the weld zone is a lamellar primary α phase, and the intragranular is a needle-shaped secondary α′ phase, both of which are evenly staggered on the β phase matrix. The volume fraction of the lamellar primary α phase is 20%, the length is 17μm, and the aspect ratio is 10:1; the volume fraction of the needle-shaped secondary α′ phase is 55%, the length is 8μm, and the aspect ratio is 12:1; the volume fraction of the β phase matrix is ​​25%. The phase difference of adjacent grains in the basketweave structure configuration is less than 10° (small-angle grain boundary) accounting for 29.3%, and greater than 10° (large-angle grain boundary) accounting for 70.7%; among them, the orientation difference in the large-angle grain boundary of the α phase is 30° accounting for 9.1%, 60° accounting for 50.1%, and 90° accounting for 40.8%. In summary, the weld zone of the TC21 titanium alloy linear friction welding joint after electric pulse treatment forms a dual-configuration basketweave structure.

[0035] Step 4: Integrate and analyze the experimental data obtained in step 3 to confirm the feasibility of this configuration in regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0036] In step 4, it was analyzed that after the electric pulse treatment, the impact toughness of the joint with the dual-configuration basket structure was greatly improved compared with the welded joint, from 16.7 J / cm 2 to 54.3 J / cm 2 , reaching 88.9% of the TC21 titanium alloy joint parent material. This configuration has an obvious effect on regulating the strengthening and toughening of TC21 titanium alloy linear friction welding joints.

[0037] Figure 1 This is a schematic diagram of the relationship between organization and toughness in the present invention. Figure 1 (a) is a schematic diagram of the microstructure and crack propagation path of the welded joint. The formation of equiaxed crystals and spherical dispersed particles in the weld zone of the joint makes the crack diffusion path straight, fast, and less branched. The energy absorbed during the destruction process is also less, so the toughness is lower. Figure 1 (b) is a schematic diagram of the joint organization and crack propagation path after electric pulse treatment. The interlaced lamellar structure in the basket organization increases the crack propagation path, and the fine needle-like organization in the crystal disperses the stress field at the crack tip, absorbs more energy, and achieves high strength and toughness of the joint. The dual-configuration basket organization configuration is initially realized through the electric pulse treatment method, which balances the advantages of high strength of equiaxed organization and good toughness of Widmanstatten organization, and has good comprehensive mechanical properties.

[0038] Figure 2 The microstructure diagram of the weld area of ​​the TC21 linear friction welding head before and after the electric pulse treatment in Example 4. Figure 2 (a) It can be seen that the weld zone of the welded joint is composed of equiaxed crystals and spherical dispersed particles within the crystals; Figure 2(b) It can be seen that after the electric pulse treatment, a dense α phase sheet structure is formed in the weld area of ​​the joint, the spherical dispersed particles in the crystal are completely transformed into fine needle-shaped secondary α′ phase, and a dual-configuration basket structure is formed in the weld area of ​​the joint.

[0039] Figure 3 This is the orientation difference distribution diagram of the TC21 linear friction welding head after electric pulse treatment in Example 4. Figure 3 It can be seen that after the electric pulse treatment, the proportion of α phase in the weld zone of the joint is 71%, the proportion of β phase is 29%, the proportion of small angle grain boundaries is 24.2%, the proportion of large angle grain boundaries is 75.8%, and the ratio of phase difference between about 60° and about 90° is approximately 3:2.

[0040] Figure 4 This is a graph of the impact toughness values ​​of the TC21 titanium alloy linear friction welding joint under different treatment methods in the present invention. Figure 4 It can be seen that after being treated under different electric pulse conditions, the impact toughness of the joint with a dual-configuration basket mesh structure is greatly improved compared with the welded joint, and the impact toughness of the joint weld area of ​​each embodiment has reached more than 88% of the toughness of the TC21 titanium alloy joint base material.

[0041] Figure 5 This is the impact fracture morphology of the TC21 linear friction welding joint before the electric pulse treatment in Example 4. Figure 5 (a) It can be seen that the impact crack propagation path of the welded joint is approximately a straight line along the welding interface, and the macroscopic fracture has obvious river-like patterns, such as Figure 5 (b) The entire fracture is divided into three areas. There are obvious cleavage planes and tear edges in the fracture initiation area, such as Figure 5 (c) shows that clear river patterns can be seen in both the crack extension zone and the shear lip zone, such as Figure 5 (d) and 5(e) show typical cleavage fracture modes.

[0042] Figure 6 This is the impact fracture morphology of the TC21 linear friction welding joint after electric pulse treatment in Example 4. Figure 6 (a) It can be seen that the U-notch of the joint impact specimen is severely deformed, the crack initiation zone is near the welding interface, the crack propagates in a zigzag manner along the thermally affected zone, the shear lip zone breaks near the welding interface, and the crack propagation path length increases significantly, indicating that the absorbed energy increases during the fracture process. Figure 6 (b) The macroscopic fracture surface of the joint is rough. Figure 6 (ce) It can be seen that the crack initiation zone, expansion zone and shear lip zone are composed of a large number of dimples. There are no cleavage planes and tear edges in the crack initiation zone and expansion zone, which is a typical ductile fracture mode. Therefore, the toughness of the joint is greatly improved.

[0043] The above examples all use TC21 titanium alloy linear friction welding joints as experimental materials. After electric pulse treatment, the weld zone of the joints forms a dual-configuration basket structure. The experimental results show that the impact toughness value of the joints with this configuration is ≥54 J / cm 2 , reaching more than 88% of the impact toughness of the joint parent material. In the prior art, the toughness of the TC21 titanium alloy linear friction welded joint that has undergone traditional heat treatment methods can reach up to 81% of the parent material toughness. It can be seen that the dual-configuration basket structure design provides a new solution for achieving high strength and toughness of titanium alloy joints.

Claims

1. A dual-configuration basket structure for improving the toughness of titanium alloy friction welded joints, characterized in that: In the structure, the grain boundary is a lamellar primary α phase and the interior of the grain is a needle-shaped secondary α′ phase, and the primary α phase and the secondary α′ phase are uniformly and alternately distributed on the β phase matrix.

2. The dual-configuration basket structure for improving the toughness of titanium alloy friction welding joints according to claim 1 is characterized in that: The volume fraction of the lamellar primary α phase is 10% to 25%, the volume fraction of the needle-shaped secondary α′ phase is 40% to 60%, and the volume fraction of the β phase matrix is ​​25% to 35%, and the total of the above volume fractions is 100%.

3. The dual-configuration basket structure for improving the toughness of titanium alloy friction welding joints according to claim 1 is characterized in that: The lamellar primary α phase has a length of 6 μm to 18 μm and an aspect ratio of 5:1 to 15:

1.

4. The dual-configuration basket structure for improving the toughness of titanium alloy friction welding joints according to claim 1 is characterized in that: The needle-shaped secondary α′ phase has a length of 3 μm to 10 μm and an aspect ratio of 10:1 to 20:

1.

5. The dual-configuration basket structure for improving the toughness of titanium alloy friction welding joints according to claim 1, characterized in that: The phase difference between adjacent grains of the basket structure is less than 10°, accounting for 20% to 30%, and greater than 10°, accounting for 70% to 80%. Among them, the orientation difference in the large-angle grain boundaries of the α phase is 30°, accounting for 5% to 15%, 60°, accounting for 45% to 55%, and 90°, accounting for 35% to 45%.

6. A method for preparing a dual-configuration basket structure for improving the toughness of a titanium alloy friction welded joint, characterized in that: Follow the steps below to implement it: Step 1, linear friction welding is performed on TC21 titanium alloy to obtain a TC21 titanium alloy sample with an original welded joint; Step 2: After pre-treating the titanium alloy sample in step 1, the sample is subjected to electric pulse treatment using preset processing parameters to form a dual-configuration basketweave structure in the joint weld area.

7. The method for preparing a dual-configuration basket structure for improving the toughness of a titanium alloy friction welded joint according to claim 6, characterized in that: The pretreatment in step 2 is specifically as follows: the titanium alloy linear friction welding sample is cut into pieces with a size of 70×12×3 mm by wire cutting technology. 3 The sample is ground on the surface by a grinder to control the surface processing accuracy within 0.01mm.

8. The method for preparing a dual-configuration basket structure for improving the toughness of a titanium alloy friction welded joint according to claim 6, characterized in that: The electric pulse treatment in step 2 is specifically as follows: the pretreated sample is fixed between two copper electrodes of the electric pulse device, and the electric pulse treatment parameter range is: pulse voltage 50V-100V, pulse frequency 200Hz-350Hz, pulse time 60s-130s, root mean square current density 6×10 6 A / m 2 ~12×10 6 A / m 2 .

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